/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
package wordsreminder;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;

/**
 * Generic unicode textreader, which will use BOM mark to identify the encoding
 * to be used.
 */
public class UnicodeReader extends Reader {
	// ~ Static fields/initializers
	// -------------------------------------------------------------------------------------

	/** TODO: DOCUMENT ME! */
	private static final int BOM_SIZE = 4;

	// ~ Instance fields
	// ------------------------------------------------------------------------------------------------

	/** TODO: DOCUMENT ME! */
	PushbackInputStream internalIn;

	/** TODO: DOCUMENT ME! */
	InputStreamReader internalIn2 = null;

	/** TODO: DOCUMENT ME! */
	String defaultEnc;

	// ~ Constructors
	// ---------------------------------------------------------------------------------------------------

	/**
	 * Creates a new UnicodeReader object.
	 * 
	 * @param in
	 *            TODO: DOCUMENT ME!
	 * @param defaultEnc
	 *            TODO: DOCUMENT ME!
	 */
	UnicodeReader(InputStream in, String defaultEnc) {
		internalIn = new PushbackInputStream(in, BOM_SIZE);
		this.defaultEnc = defaultEnc;
	}

	// ~ Methods
	// --------------------------------------------------------------------------------------------------------

	/**
	 * @todo DOCUMENT ME!
	 * 
	 * @return TODO: DOCUMENT ME!
	 */
	public String getDefaultEncoding() {
		return defaultEnc;
	}

	/**
	 * @todo DOCUMENT ME!
	 * 
	 * @return TODO: DOCUMENT ME!
	 */
	public String getEncoding() {
		if (internalIn2 == null) {
			return null;
		}

		return internalIn2.getEncoding();
	}

	/**
	 * Read-ahead four bytes and check for BOM marks. Extra bytes are unread
	 * back to the stream, only BOM bytes are skipped.
	 * 
	 * @throws IOException
	 *             TODO: DOCUMENT ME!
	 */
	protected void init() throws IOException {
		if (internalIn2 != null) {
			return;
		}

		String encoding;
		byte[] bom = new byte[BOM_SIZE];
		int n;
		int unread;
		n = internalIn.read(bom, 0, bom.length);

		if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB)
				&& (bom[2] == (byte) 0xBF)) {
			encoding = "UTF-8";
			unread = n - 3;
		} else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {
			encoding = "UTF-16BE";
			unread = n - 2;
		} else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {
			encoding = "UTF-16LE";
			unread = n - 2;
		} else if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00)
				&& (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF)) {
			encoding = "UTF-32BE";
			unread = n - 4;
		} else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)
				&& (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00)) {
			encoding = "UTF-32LE";
			unread = n - 4;
		} else {
			// Unicode BOM mark not found, unread all bytes
			encoding = defaultEnc;
			unread = n;
		}

		if (unread > 0) {
			internalIn.unread(bom, (n - unread), unread);
		} else if (unread < -1) {
			internalIn.unread(bom, 0, 0);
		}

		// Use given encoding
		if (encoding == null) {
			internalIn2 = new InputStreamReader(internalIn);
		} else {
			internalIn2 = new InputStreamReader(internalIn, encoding);
		}
	}

	/**
	 * @todo DOCUMENT ME!
	 * 
	 * @throws IOException
	 *             TODO: DOCUMENT ME!
	 */
	public void close() throws IOException {
		init();
		internalIn2.close();
	}

	/**
	 * @todo DOCUMENT ME!
	 * 
	 * @param cbuf
	 *            TODO: DOCUMENT ME!
	 * @param off
	 *            TODO: DOCUMENT ME!
	 * @param len
	 *            TODO: DOCUMENT ME!
	 * 
	 * @return TODO: DOCUMENT ME!
	 * 
	 * @throws IOException
	 *             TODO: DOCUMENT ME!
	 */
	public int read(char[] cbuf, int off, int len) throws IOException {
		init();

		return internalIn2.read(cbuf, off, len);
	}
}
